1. Field of the Invention
The present invention relates to plasma assisted chemical processing and, in particular to the use of non-thermal capillary discharge plasma (NT-CDP) or a non-thermal slot discharge plasma (NT-SDP) (collectively referred to as “NT-CDP/SDP”) to energize specific chemical species in a more homogeneous manner than traditional discharge technologies (e.g., Arc, gliding Arc, Dielectric Barrier Discharge (DBD) and Corona) allowing for higher yield and greater energy efficient chemical conversion. Unlike traditional discharge technologies which tend to create filamentary discharges that are spatially and temporally inhomogeneous a NT-CDP/SDP device generates a diffuse stable plasma with a minimum of volume inefficiencies to help insure equivalent treatment. The NT-CDP/SDP device can also be specifically tuned to selectively initiate certain rate determining chemical reactions, which readily cascade toward the desired product. Adding energy to the system in this specific manner enables chemical reactions to take place under ambient conditions that ordinarily would only be possible at higher temperatures and pressures. Tuning is accomplished by varying: the power, reactant composition and concentration, carrier gas composition and flow rate, temperature, pressure and/or reactor geometry.
2. Description of Related Art
The use of an electrical discharge to initiate chemical reactions of industrial importance has been known and used for a long time. One of the oldest and most efficient chemical transformations that occur in the presence of an electrical discharge is the generation of ozone. The generated ozone may be reacted with unsaturated hydrocarbons to synthesize ozonides, aldehydes, and ketones. Typical early gas discharge devices operate by exposing different reactant gases to an electrical Arc (thermal plasma), as described by Knight, Henry de Boyne, The arc discharge, its application to power control, London, Chapman & Hall (1960).
Recent advances have made use of both thermal and non-thermal plasma in chemical processing. U.S. Pat. No. 6,372,192 to Paulauskas et al. describes a process for carbon fiber manufacturing using plasma. In this patented process, stabilized polyacrylonitrile (PAN) fiber, the first step in carbon fiber processing, is converted to carbon graphite fiber using GHz frequency plasma in a low-pressure oxygen free atmosphere. This patent, however, does not disclose or suggest using oxygen rich plasma to stabilize PAN fibers in the initial step of the process.
Research and development in the field of plasma assisted fuel reforming and fuel conversion has also made significant progress in recent years, due predominantly to renewed interest in hydrogen fuel cells. For instance, U.S. Pat. No. 6,322,757 to Cohn et al. and the references cited therein disclose a plasma fuel converter such as a plasmatron to reform hydrocarbons to produce a hydrogen rich gas. U.S. Pat. No. 6,395,197 to Detering et al. describes a high temperature apparatus and method for the thermal conversion of light hydrocarbons (natural gas) to desired end products, particularly diatomic hydrogen and elemental carbon. Yet another patented invention, U.S. Pat. No. 6,375,832 to Eliasson et al., teaches a method for the chemical transformation of a hydrogen (such as methane) and carbon (such as carbon dioxide) rich gas into a normally liquid fuel. This plasma assisted Fischer-Tropsch synthesis is conducted by using a dielectric barrier discharge in conjunction with a solid zeolite catalyst.
Another area of plasma processing that has received significant attention is plasma activated surface treatment of polymeric materials to increase wetability and/or surface adhesion, for example, as described in the publication by L. A. Rosenthal and D. A. Davis entitled “Electrical Characterization of a Corona Discharge for Surface Treatment”, IEEE Transaction on Industry Applications, vol. 1A-11 No. 3, pp. 328-335 (May/June 1975), the publication by S. Han, Y. Lee, H. Kim, G. Kim, J. Lee, J. Yoon, G. Kim, entitled “Polymer Surface Modification by Plasma Source Ion Implantation”, Surfaces & Coatings Technology, vol. 93, pp. 261-264 (1997), and U.S. Pat. No. 6,399,159 to Grace et al.
It is therefore desirable to optimize chemical processing through the use of a NT-CDP/SDP, as described in U.S. Pat. No. 09/738,923, filed on Dec. 15, 2000 and 60/358,340, filed on Feb. 19, 2002, each of which are hereby incorporated by reference in their entirety.